Asthma is one of the leading causes of morbidity in children with the majority of all cases diagnosed in early childhood and over 56 billion dollars in health costs annually. Thus, finding factors that can lead to prevention of this disease would be of great public health importance. Vitamin D deficiency is highly prevalent among pregnant women, and thus, represents a potentially modifiable factor for the prevention of disease. Due to the effect of vitamin D in the development of the lung and the immune system in utero, we believe that vitamin D deficiency in pregnant mothers leads to increased risks for developing asthma and allergy in early childhood. Epidemiologic studies that have investigated the role of vitamin D in early life and the development of asthma, wheeze and allergy have inconsistent results. Because of the wide prevalence of vitamin D deficiency, a clinical trial is the only way t confidently answer the question of whether higher vitamin D levels in pregnancy can prevent asthma and allergies in the mother's offspring. Over the past 4 years, we have been conducting a randomized, placebo-controlled trial of maternal vitamin D supplementation in pregnancy, and we are now following the children (ClinicalTrials.gov Identifier: NCT00920621). We recruited 881 women, and randomized them to one of two arms: 4,000 IU vitamin D3 daily plus a prenatal vitamin containing 400 IU vitamin D3 vs. a placebo plus a prenatal vitamin containing 400 IU vitamin D3. We followed them through pregnancy and there were 810 live births with 801 currently under follow-up. The goal of the current project is to follow the children through age 6 years. The specific aims for the renewal of VDAART are: (1) to determine whether maternal supplementation of vitamin D during pregnancy is associated with reduced incidence of asthma in the child during the first 6 years of life; (2) to determine whether maternal supplementation of vitamin D during pregnancy is associated with reduced secondary outcomes in the child of: (a) allergic sensitization (total and specific IgE), (b) doctor's diagnosis of eczema, (c) doctor's diagnosis of allergic rhinitis, (d) food allergies and (e) lower respiratory tract infections by ag 6 years; (3) to determine whether maternal supplementation of vitamin D during pregnancy is associated with greater lung growth in the children up to age 6, as measured by impulse oscillometry and spirometry; and (4) to continue to collect biologic material from the children for mechanistic studies related to vitamin D in asthma and allergies, including specimens for genomic and epigenomic studies and microbiome studies. Findings from this important study will have great public health importance in the prevention of asthma and allergies in childhood.